Just had noisy blower motor assembly replaced on 1989 Grand Wagoneer
Air comes through vents when AC selected. Air doesn't come through vents when heat and/or defrost is selected. Can feel heat on the floor under the dash but again no heat coming through the vents.
There are vacuum operated doors that direct heat. Check for a vacuum leak in the hoses and see if the hoses are hooked to the motors.
Search Jeep Grand Wagoneer Questions
Jeep Grand Wagoneer Experts